Magnetic work holder



Feb. 3, 1942. E. l.. wA'TELET MAGNETIC WORK HOLDER Filed Aug. 5, 1940 82.62% qww A TTORNEYS.

VPatented Feb. 3, 1942 MAGNETIC wom; HoLnEa Ermand L. Watelet, Greenwood, R. I., assignor to Brown & Sharpe Manufacturing Company, a corporation of Rhode Island Application August 3, 1940, Serial No. 350,620

(Cl. F75- 367) 4 Claims.

This invention relates to a magnetic work holder of that type utilizing shiftable permanent magnets which, in one position will cause a mag'- netic iiux to pass through pole ypieces and through the work to holdthe work, or in another position, .'will cause the magnetic ux to be shunted for the establishment of .an auxiliary circuit so as to pass through a path different from the work that the work may be released and readily removed from the holder.

One of the objects of this invention is to provide an arrangement whereby the movable magnet may be more easily shifted from one position to the other which is of very material importance when larger magnetic work holders are utilized.

Another object oi the invention is to space the shiftable magnet from the top plate and pole pieces carried thereby so as to relieve any friction of these parts rubbing one on the other when moved and to provide rolling means between the two for movement of one relative to the other.

.Another object of the invention is to provide some means to neutralize the force tending to move the pack to the oil! position.

With these and other objects in View, the invention consists of certain novel features of construction, as will be more fully described, and particularly pointed out in the appended claims.

In the accompanyingdrawing: y

Fig. 1 isa top plan view partially broken away and in section to illustrate the interior of the magnetic work holder;

Fig. 2 is a section on substantially line 2--2 of Fig. 1;

Fig. 3 is a section on substantially line 3--3 of Fig. 1;

Fig. 4 is a section on substantially line 4 4 of Fig. 1; v l

Fig.-5 is a fragmenta'l section of a portion of the pack shifted to a position different from` that shown in Fig. 4. Y

Magnetic work holders of the permanent magnet type are limited to some extent in the size inherent in such a structure and to make the4 shifting of the magnetic pack with reference to the work holder plate more easily accomplished and also to overcome to some extent the tendency toward movement of the pack with reference to the plate carrying the pole pieces, I have caused a thrust of the pack toward the plate which engages the work due to the magnetic attraction of one for the other to act through anti-friction means, such for instance, as ball bearings, and I have provided resilient means to overcome the tendency of the pack to move from alignment with the pole pieces to the position where the circuit is closed through the platebut not through the work; and the following is a more detailed descriptionv of the present embodiment of this/invention, illustrating the preferred means by which these advantageous results may be accomplished.

With reference to the drawing, I0 designates the top plate which may be of iron of good permeability through which magnetic flux will pass and in which there are positioned a plurality of pole pieces II, each separatedy from the general body portion of the plate by some magnetically insulating material I2', such as lead or solder or other non-ferrous material.

ing of magnetic ilux therethrough. The mag-v nets I1 are insulated from the bars I8 by some suitable means such for instance ras air with spacing washers 45. 'I'he pack thus made up of alternating magnets and iron bars of high permeability are bolted'together by longitudinallyextending bolts I9 headed as at 20 and threaded into the end member 2I for securing the pack in assembled relation. This pack also has a base plate 22 which is assembled with the pack by bolts 23a. This pack is free to move longitudinally of the hollow box-like casing above mentioned and is guided in such movement by a rail 23 secured to the base I3 by a bolt 24 and tting within a recess 25 in the base 22. There is an inherent'tendency due to the magnets and the magnetic flux passing Qualities of the topplate to cause the pack to lift or move toward the top plate, and ordinarily in devices of this character, an engagement of these two will occur so that shifting movement is resisted by the friction developed due to such engagement. However, in order to provide a mounting of the balls.

which will permit of easier rectilinear movement, I have secured a thrust rail 28 preferably of non'- magnetic material to each side of the bottom face of the top plate I by means of bolts 21 and have mounted a wear strip or track 2l along its under surface. The base plate 22 is of a width greater than the magnets I1 and flux-conductor bars Il to extend on either side beneath this thrust-bar 28 and upon this underlying portion 2l ofrwthe pack I support the ball race 30 having balls 3i which engage the wear strip 2B and also the wear strip l2 secured to the portion 29 of this base. The dimensions of these wear strips, which are of hardened material, plus the diameter of the balls and the dimensions of the thrust bars 26 are such as to slightly space the magnets and bars l1 and Il from the top plate as at Il. 'Ihe bearings are sufliciently close together to prevent flexing of the top plate which otherwise might occur due to the strong magnetic force. 'I'he pack is thus sustained by its own attraction in spaced relation from the top plate, while it is mounted so that relative shifting of the pack, so suspended, will occur through the rolling contact tively easy movement of the parts may occur. The ball race is slotted as at I4 and pins I5 fixed in the ends of the thrust bars 26 vserve. to guide this ball race with reference to the top plate.

The movement of the pack with reference to the top plate is through the shaft 35a and crank handle 36-31 for manual engagement to rotate the eccentric 38 on the end of the shaft 35a which extends into the link Il connected by pin 4l to the pack to rock with reference thereto. When the magnets are in the position shown in Fig. 4. the work Il will be held in position by reason of the magnetic flux indicated as at l2 passing through the bar IB and the magnet l1 and through the pole piece H andthe work to hold the work in position. If, however, the pack is shifted to the position shown in Fig. 5, then the magnetic flux 42 will bypass the work, passing through the portion 43 of the top plate, and the work will be free tobe lifted from position.

When the work is in position,` due to magnetic flux leakage, there is a tendencyfor the pack to shift from the position shown in Fig. 4, tothe position shown in Fig. and in order to avoid such shifting, compression springs 44 are provided at one end of the hollow casing so as to hold the pack in the position shown in Fig. 4 when shifted thereto, which position is at the limit of the movement of the magnetic Pack.

By the above arrangement, the advantages of having a closed magenticilux circuit when the device is not in use are provided. Permanent magnets are utilized, having their desirable qualities, which may be shifted for holding or for releasing the work, while this shifting is made easy by the anti-friction suspension of the pack in position.`

I claim:

1. A magnetic work holder comprising a work# engaging plate, spaced pole pieces mounted in said plate andl magnetically insulated one from the other, a movable unit associated `:vith said plate having a pack formed or spaced permanent magnets of sufficient magnetic force to ilex the work plate toward the unit when the work is held on the plate and with the magnets so positioned as to register the magnets with magnetic areas of the composite top plate to establish a By reason of this suspension rela-- magnetic circuit for passing magnetic flux through the work. the lower portion of the plate and the upper portion of the unit having spaced but closely adjacent surfaces, means to support the plate and unit in their spaced relationship' plate having a pack formed of spaced permanent magnets of sufllcientmagnetic force to flex the work plate toward the unit when the work is held on the plate and with the magnets so positioned as to register the magnets with magnetic areas of the composite top plate to establish a magnetic circuit for passing magnetic flux through the work, the lower portion of the plate and the upper portion of the unit having spaced but closely adjacent surfaces, anti-friction rolling bearings for supporting the plate and unit in their spaced relationship, said bearings being closely spaced and positioned in rows along the path of movement between portions fixed relatively to the plate and portions of the movable unit so as to prevent iiexure of the plate.

3. A magnetic work holder comprising a workengaging platel spaced pole pieces mounted in said plate and magnetically insulated one from `the other, a longitudinally slidable unit associated with said plate having a pack formed of spaced permanent magnets having suiiicient magnetic force to flex the work plate toward the unit when the work is held on the plate and so positioned as to register the magnets with magnetic areas of the composite top plate, when in one position to establish a magnetic circuit for passing magnetic ux through the work, the lower portion of the plate and the upper portion of the unit having relatively longitudinally movable surfaces, anti-friction rolling bearings carried by said pack and located closely adjacent to each other throughout the longitudinal extent of the unit and a thrust bar carried by and depend ing from said plate and with its engaging surface positioned a distance from said plate to engage said bearings and 'closely space said surfaces while supporting the plate to prevent fiexure toward the magnet unit.

4. A magnetic work holder comprising a workengaging plate, spaced pole pieces mounted in said plate and magnetically insulated one from the other, a movable unit associated with said plate having a pack formed of spaced permanent magnets of suiiicient magnetic force to flex the work plate toward the unit when the Work is held on the plate and with the magnets so positioned as to register the magnets with magnetic areas of the composite top plate to establish a magnetic circuit for passing magnetic flux through the work, the lower portion of the plate and the upper portion of the unit having spaced but closely adjacent surfaces, means to support the plate and unit in their spaced relationship comprising rolling bearings so closely spaced and positioned along thepath of movement as to prevent flexure of the plate, and resilient means to press against said unit in a direction to oppose the tendency of the pack to shift from work holding position to work releasing position.

ERMAND L. WA'I'ELET. 

